Fortunately, Google is now working, so when I did a search, I discovered this essay:
http://www.sillymagic.com/essayitsnotthe.htm
The original tricks were by the long-gone Supreme Magic Company, but David Kaye mentions a similar product,
Pet Store Pranks. A further search revealed a few suppliers, including Magic Nevin:
http://www.magicnevin.com/proddetail.asp?prod=JM00130
If you must have the zoo one, good luck in finding what is apparently a rare item. You could always try advertising for a set.
There's also this DVD, which apparently deals with the trick:
http://www.magictricks.co.uk/products/1 ... Shoesmith/